[Offline Pages] Set up the initial prefetching service.

components/offline_pages/content/suggested_articles_observer.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/offline_pages/content/suggested_articles_observer.h"
+
+#include <unordered_set>
+
+#include "base/memory/ptr_util.h"
+#include "components/ntp_snippets/category.h"
+#include "components/ntp_snippets/category_status.h"
+#include "components/offline_pages/content/prefetch_service_factory.h"
+#include "components/offline_pages/core/client_namespace_constants.h"
+#include "components/offline_pages/core/offline_page_feature.h"
+#include "components/offline_pages/core/prefetch/prefetch_service_impl.h"
+
+using ntp_snippets::Category;
+using ntp_snippets::ContentSuggestion;
+
+namespace offline_pages {
+
+namespace {
+
+int kOfflinePageSuggestedArticlesObserverUserDataKey;
+
+const ntp_snippets::Category& ArticlesCategory() {
+  static ntp_snippets::Category articles =
+      Category::FromKnownCategory(ntp_snippets::KnownCategories::ARTICLES);
+  return articles;
+}
+
+ClientId CreateClientIDFromSuggestionId(const ContentSuggestion::ID& id) {
+  return ClientId(kSuggestedArticlesNamespace, id.id_within_category());
+}
+
+// The default delegate that contains external dependencies for the Offline Page
+// Suggestions Observer.  This is unused in tests, which implement their own
+// Delegate.
+class DefaultDelegate : public SuggestedArticlesObserver::Delegate {
+ public:
+  explicit DefaultDelegate(ntp_snippets::ContentSuggestionsService* service);
+  ~DefaultDelegate() override = default;
+
+  const std::vector<ContentSuggestion>& GetSuggestions(
+      const Category& category) override;
+  PrefetchService* GetPrefetchService(
+      content::BrowserContext* context) override;
+
+ private:
+  ntp_snippets::ContentSuggestionsService* service_;
+};
+
+DefaultDelegate::DefaultDelegate(
+    ntp_snippets::ContentSuggestionsService* service)
+    : service_(service) {}
+
+const std::vector<ContentSuggestion>& DefaultDelegate::GetSuggestions(
+    const Category& category) {
+  return service_->GetSuggestionsForCategory(category);
+}
+
+PrefetchService* DefaultDelegate::GetPrefetchService(
+    content::BrowserContext* context) {
+  return PrefetchServiceFactory::GetForBrowserContext(context);
+}
+
+}  // namespace
+
+// static
+void SuggestedArticlesObserver::ObserveContentSuggestionsService(
+    content::BrowserContext* browser_context,
+    ntp_snippets::ContentSuggestionsService* service) {
+  if (!offline_pages::IsPrefetchingOfflinePagesEnabled())
+    return;
+
+  auto suggestions_observer = base::MakeUnique<SuggestedArticlesObserver>(
+      browser_context, base::MakeUnique<DefaultDelegate>(service));
+  service->AddObserver(suggestions_observer.get());
+  service->SetUserData(
+      &kOfflinePageSuggestedArticlesObserverUserDataKey,
+      // Note that |service| will take ownership of suggestions_observer
+      // despite accepting a raw pointer.
+      suggestions_observer.release());
+}
+
+SuggestedArticlesObserver::SuggestedArticlesObserver(
+    content::BrowserContext* browser_context,
+    std::unique_ptr<Delegate> delegate)
+    : browser_context_(browser_context), delegate_(std::move(delegate)) {}
+
+SuggestedArticlesObserver::~SuggestedArticlesObserver() = default;
+
+void SuggestedArticlesObserver::OnNewSuggestions(Category category) {
+  if (category != ArticlesCategory() ||

[jkrcal, 2017/04/21 13:57:06]

This special-casing to KnownCategories::ARTICLES is unfortunate. We run and plan
to run various server-side experiments with providing other remote categories
(with different IDs). There are conceptually articles to be prefetched, just not
ARTICLES.

Please add a TODO to change this to check whether a given category is not a
_remote_ category. This involves changes in category.h, so lets leave it for a
follow-up CL.

[dewittj, 2017/04/21 21:59:04]

Done.

+      category_status_ != ntp_snippets::CategoryStatus::AVAILABLE) {
+    return;
+  }
+
+  const std::vector<ContentSuggestion>& suggestions =
+      delegate_->GetSuggestions(ArticlesCategory());
+  if (suggestions.empty())
+    return;
+
+  std::vector<PrefetchService::PrefetchURL> prefetch_urls;
+  for (const ContentSuggestion& suggestion : suggestions) {
+    prefetch_urls.push_back(
+        {CreateClientIDFromSuggestionId(suggestion.id()), suggestion.url()});
+  }
+
+  PrefetchService* service = delegate_->GetPrefetchService(browser_context_);

[jkrcal, 2017/04/21 13:57:07]

Shouldn't you check for nullptr?
Does the factory always create the service? What about incognito profile? In
incognito profile there is also no content suggestions service. I am just
wondering whether the guarantees are not too subtle.

[dewittj, 2017/04/21 21:59:04]

Done.

+  service->AddCandidatePrefetchURLs(prefetch_urls);
+}
+
+void SuggestedArticlesObserver::OnCategoryStatusChanged(
+    Category category,
+    ntp_snippets::CategoryStatus new_status) {
+  if (category != ArticlesCategory() || category_status_ == new_status)
+    return;
+
+  category_status_ = new_status;
+
+  if (category_status_ ==
+          ntp_snippets::CategoryStatus::CATEGORY_EXPLICITLY_DISABLED ||
+      category_status_ ==
+          ntp_snippets::CategoryStatus::ALL_SUGGESTIONS_EXPLICITLY_DISABLED) {
+    PrefetchService* service = delegate_->GetPrefetchService(browser_context_);

[jkrcal, 2017/04/21 13:57:07]

ditto

[dewittj, 2017/04/21 21:59:04]

Done.

+    service->RemoveAllUnprocessedPrefetchURLs(kSuggestedArticlesNamespace);
+  }
+}
+
+void SuggestedArticlesObserver::OnSuggestionInvalidated(
+    const ContentSuggestion::ID& suggestion_id) {
+  PrefetchService* service = delegate_->GetPrefetchService(browser_context_);
+  service->RemovePrefetchURLsByClientId(
+      CreateClientIDFromSuggestionId(suggestion_id));
+}
+
+void SuggestedArticlesObserver::OnFullRefreshRequired() {
+  PrefetchService* service = delegate_->GetPrefetchService(browser_context_);
+  service->RemoveAllUnprocessedPrefetchURLs(kSuggestedArticlesNamespace);
+  OnNewSuggestions(ArticlesCategory());
+}
+
+void SuggestedArticlesObserver::ContentSuggestionsServiceShutdown() {
+  // No need to do anything here, we will just stop getting events.
+}
+
+}  // namespace offline_pages